Atherosclerosis is a major cause of cardiovascular disease in developed countries. In this disorder, endothelial cells acquire procoagulant properties, while activated smooth muscle cells and macrophages accumulate in the arterial wall. The overall objective of this project will be to understand the regulation of the annexin 2 (A2)-based proteolytic cascade, initiated by plasmin, on the surface of vascular cells. A2 is a major profibrinolytic receptor expressed on endothelial cells, activated smooth muscle cells, and macrophages. A2 accelerates plasmin generation by several orders of magnitude, and plays a central role in directed vascular cell migration and matrix remodeling, through the activation of additional downstream proteases. Preliminary data suggest that translocation of A2 to the cell surface is a primary mechanism by which vascular cells (endothelial cells, smooth muscle cells, and macrophages) upregulate cell surface proteolytic activity. In this proposal, we will elucidate the molecular pathways that govern the transport of A2 to the cell surface in response to stress and/or injury to vascular cells. Previously, we demonstrated that A2 is exported from a cytoplasmic compartment to the cell surface through a non-classical, Golgi/endoplasmic reticulum-independent pathway initiated by brief heat stress. We showed that this regulated response requires the participation of the A2 binding protein, p11 (S100A10), which enables a src-like, kinase- mediated tyrosine-23 phosphorylation switch that initiates the translocation response. In the proposed studies, we will examine [1] the mechanism by which endothelial cells, smooth muscle cells, and macrophages translocate A2 to the cell surface in response to injury, [2] the role of the ATP binding cassette transporter A1 (ABCA1) in this process, [3] the specific role of the A2-binding protein, p11, in A2 translocation, and [4] the significance of A2 transport in the response to vascular injury in vivo. These studies will utilize combined approaches involving in vitro culture systems and genetically modified mouse models, including A2 and p11 -nulls created in our laboratory. We will continue to collaborate with investigators in Projects III and V to capitalize on their expertise in the study of the growth factor signalling and cholesterol transporter mechanisms.